Piezoelectric Accelerometers and Vibration Preamplifiers

Piezoelectric Acceleromete and Vibration Preamplifiers
Theory and Application Handbook
Briiel & Kjar
Mark Senldge, BSc
TorbenR. Llcht, MSc
CONTENTS
1. V|BRAT|ONiTEASUREMENT . 1
1.1.TNTRODUCTTON 1
1.2.WHY MEASUREVIBRATTON? . 1
1.3.WHATtS V|BRAT|ON? 5
1.4.V|BRAT|ONPARAMETERS . 6
1.5.THE QUANTIFICATION OF VIBRATIONLEVELS 7
Linearamplitudeand frequencyscales . I
Logarithmicamplitudeand frequencyscales . I
1.6.ANALYSISOF VIBRATIONMEASUREMENTS 11
2. THE PIEZOELECTRICACCELEROiIETER
2.1.fNTRODUCTION . ‘t2
2.2.OPERATTON OF AN ACCELEROMETER . 13
Analyticaltreatmentol accelerometeroperation . 14
2.3.FREQUENCYRANGE .; . 18
Upperfrequencylimit 19
Lower frequencylimit 20
2.4.PIEZOELECTRIC MATERTALS . 20
2.5.PRACTICALACCELEROMETERDESIGNS 22
Line-driveaccelerometers
Other designs . 25
2.6.ACCELEROMETERSENSITIVITY . 25
Chargeand voltagesensitivity 26
Uni-Gainosensitlvity 28
Linearityand dynamlcrange 28
Transversesensltlvlty 29
2.7.PHASERESPONSE 30
2.8.TRANSTENT RESPONSE . . 33
Leakageeffects 33
Ringing . 35
12
Zero shift . 373. VIBRATIONPREAMPLTFTERS . . 38
3.1.PREAMPLTFTER DESTGNAND OPERATTON , 39
3.2.CHARGEAMPLIFIERS ., . 39
Chargesensitivity . 40
Lower LimitingFrequency .44
Capacitiveloadingof input by accelerometercables . 48
Chargeattenuation , . 49
Nolsein chargeamplifiers 50
3.3.VOLTAGEPREAMPLTFTERS . . 54
Voltagesensitivity 55
Lower LimitingFrequency .56
Noisein voltagepreamplifiers 57
3.4.PREAMPLIFIEROUTPUTCABLES . 57
3.5.L|NE-DRTVE SYSTEMS . 58
Br0el&Kjer line-driveaccelerometerand line-drivesupply . 61
BrUel &Kjer line-driveamplifierand line-drivesupply . 61
3.6.COMPARISONOF THE SENSITIVITYOF DIFFERENT
VIBRATIONPREAMPLIFIERSYSTEMSTO
EXTERNALNO|SESOURCES . 61
Groundedaccelerometerand chargepreamplifier ‘ O+
Groundedaccelerometerwith chargepreamplifier
(“floating”input) . 65
Brriel&Kjar line-driveamplifierand power supply
(groundedinput) . 66
BrUel & Kjar line-driveamplifierand power supply
(“floating”input) . 68
Line-drive system based on constant current
powersupply . 70
Balancedaccelerometerand differentialcharge
amplifier 69
fnsufatedmountingof the accelerometer .- . 71
3.7.SPECTALPREAMPLTFTER FEATURES 71
fntegrationNetworks . 72
Filters 76
Overloadlndicator . 78
ReferenceOscillator .- 78
PowerSupplies . 78
ACCELEROMETERPERFORMANCEtN PRACTTCE 79
4.1.INTRODUCTTON 79
4.2.ENVTRONMENTAL EFFECTS . 80
Temperaturerange . . 80
Temperaturetransients .82Acousticsensitivity ‘ ‘ 84
Basestrains ‘ .” .’. 85
Humidity .’ -. 85
Magneticsensitivity . 86
Radiation .’ .’ . 86
4.3.MASS LOADINGEFFECTSOF ACCELEROMETERS . 86
4.4.MOUNTTNG THE ACCELEROMETER . . 88
Vibrationtest surfacefinish requirements ‘. 89
Mountinglocation ‘ ‘ . 89
Determinationof the frequency responseof accelerometers
using differentmountingtechniques ‘ ‘.90
Stud mountinS . .’ ‘ .’ 90
Wax mountinS .’ .’ ‘ ‘ ” ‘. 93
Magneticmounting .’ ‘ 95
Self-adhesivemountingdiscs . .’97
Adhesives .’ 98
Probes 102
4.5.MECHANICALFILTERS 105
Description 105
Operation .’106
4.6.ACCELEROMETER CABLES . 107
4.7.GROUNDTNG PRECAUTIONS 109
ACCELEROMETERCALIBRATIONAND TESTING . 111
5’1′ lNTRoDUcrloN “”””””””” 111
Why calibratean accelerometer? .’.- 113
5.2.THE HIERARCHYOF CALIBRATIONSTANDARDS 114
The generalhierarchy .’ .114
The hierarchyat B&K .’ ‘ . 115
The accuracyol calibrationtechniques 118
5.3.CALTBRATION METHODS . . 119
Laser Interferometery .’ 119
Other absolutemethods ‘ ‘ .’ 121
Comparison calibration by the
“back-to-back”method “. 121
FFT-basedback-to-back calibration ‘- -123
The use of calibrated vibration exciters
for sensitivitychecking .” 124
5.4.MEASUREMENTOF OTHERACCELEROMETERPARAMETERS 125
Transversesensitivity .’ ” 125
Frequencyresponse ‘ 126
Undampednaturalfrequency ‘ .’. 128
Capacitance .- .” 1296.
5.5.DETERMINATION OF THE EFFECTSOF THE ENVIRONMENT
oN THE ACCELEROMETERSPECTETCATTONS . 129
Temperaturetransientsensitivity . 129
Temperaturesensitivity .129
Base strain sensitivity .130
Acousticsensitivity 130
Magneticsensitivity . 131
Temperaturelimits . 131
Shocklimits . 132
5.6.FACTORYTESTINGOF ACCELEROMETERCABLES 132
5.7.CALTBRATTON EQUTPMENT . 133
CalibrationSystemType 9559 133
Individualcalibrationequipment 133
5.8.STANDARDSRELATINGTO THE CALIBRATION
oF ACCELEROMETERS 134
APPENDTCES . 137
APPENDIXA. Conversioncharts . 138
APPENDIXB. Vibrationnomogram . 141
APPENDIXC. Vibrationstandards . 142
APPENDfXD. BrUel&KjerVibrationLiterature . 142
APPENDIXE. Summaryof Bruel&Kjer Preamplifiers 144
APPENDIXF.Summaryof BrUel &Kjar instruments
with built-in preamplifiers 146
APPENDIXG. BrUel&Kjar accelerometerfrequencyand dynamic
rangecharts 148
APPENDIXH. Summaryof BrUel & Kjar accelerometers .
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